1. Field of the Invention
The subject matter of the invention is an ionic current measuring glow plug and process and circuit for its activation.
2. Description of Related Art
Generic glow plugs have a glow tube or an equivalent component in which there is a heating element, the glow tube being insulated relative to the plug housing and the plug housing being electrically connected to the engine block (ground).
A glow plug which is designed for glowing and measurement of the ionic current must be made such that at least in the area of the glow plug tip it represents a measurement electrode to which an auxiliary voltage UH can be applied. This voltage is then between the electrode and the inside wall of the cylinder. If at this point ions are produced by the combustion process, current flows. Its behavior allows conclusions to be drawn about the combustion process in the cylinder.
Preferably the glow plug is made such that the glow plug tip can be used as an electrode; in this case the heating element and the electrode are electrically interconnected; at the same time the electrode and the heating element are electrically insulated against the glow plug body. These glow plugs conventionally have two electrical terminals with which the glow plug is connected to a control device. The previously described conventional system for glowing and ionic current measurement has several serious defects:
The glow plugs used for ionic current measurement must be connected bipolarly; on the glow plug a new plug-in system is necessary. A corresponding connector must have two heavy current contacts and is thus more expensive than the single pole version.
Plugging a bipolar mating connector onto the engine block-mounted glow plug is more complex than plugging on a rotationally symmetrical connector.
Feedback of the glow plug current to the control device requires a second heavy current line with a large cable cross section with a corresponding plug-and-socket connection on the control device. In this way added costs arise in the control device and due to the additional cable.
The second heavy current line together with the resulting additional contact points increases unwanted contact resistances, reducing the voltage on the glow plug.
In the control device, in addition to the heavy current terminal which is always present in the plus line (current load: total of all glow plug currents) which is usually made as a screw terminal, another heavy current terminal in the minus line is necessary; here added costs arise in installation.
To overcome these defects the object of the invention consists in making available new glow plugs for glowing and for measurement of the ionic current, and new glow plug control devices and new glow plug control circuits for proper operation of glow plugs with ionic current measurement function.
The invention is explained in detail using the following FIGS. 1 to 4.